THS1041CPWR datasheet(17/42 Pages) TI1

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THS1041

SLAS289C − OCTOBER 2001 − REVISED OCTOBER 2004

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PRINCIPLES OF OPERATION

ADC reference generation

The THS1041 ADC references REFT and REFB can be driven from external (off-chip) sources or from the

internal A2 reference buffer. The voltage at the MODE pin determines the ADC references source.

Connecting MODE to AGND enables external ADC references mode. In this mode the internal buffer A2 is

powered down and the user must provide the REFT and REFB voltages by connecting external sources directly

to these pins. This mode is useful where several THS1041 devices must share common references for best

matching of their ADC input ranges, or when the application requires better accuracy and temperature stability

than the on-chip reference source can provide.

Connecting MODE to AVDD or AVDD/2 enables internal ADC references mode. In this mode the buffer A2 is

powered up and drives the REFT and REFB pins. External reference sources should not be connected in this

mode. Using internal ADC references mode when possible helps to reduce the component count and hence

the system cost.

When MODE is connected to AVDD, a buffered AVDD/2 voltage is also available at the CLAMPOUT pin. This

voltage can be used as a dc bias level for any ac-coupling networks connecting the input signal sources to the

AIN+ and AIN− pins.

MODE PIN

REFERENCE SELECTION

CLAMPOUT PIN FUNCTION

AGND

External

Clamp

AVDD/2

Internal

Clamp

AVDD

Internal

AVDD/2 for AIN± bias

external reference mode (MODE = AGND)

Sample

and

Hold

X−1

ADC

Core

PGA

AIN+

AIN−

Internal

Reference

Buffer

VREF

REFT

REFB

Figure 26. ADC Reference Generation, MODE = AGND

Connecting pin MODE to AGND powers-down the internal references buffer A2 and disconnects its outputs

from the REFT and REFB pins. The user must connect REFT and REFB to external sources to provide the ADC

reference voltages required to match the THS1041 input range to their application requirements. The

common-mode reference voltage must be AVDD/2 for correct THS1041 operation:

(REFT

) REFB)

(7)

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